Preheat oven to 350°. Grease and flour a 8-inch x 12-inch baking dish.

Beat egg in large bowl. Add sweet rice flour, stirring until combined. Add baking powder, sugar, and walnuts, mixing thoroughly.

Gently stir in red beans. Add milk and stir to combine.

Pour mixture into baking dish and bake 50-60 minutes, until toothpick inserted in center comes out clean.